Transcript Herbicide Resistant Weeds and Their Management Eric P

Herbicide Resistant Weeds
and Their Management
Eric P. Prostko and A. Stanley Culpepper
Extension Weed Specialists
The University of Georgia
Updated October 2005
Herbicide Resistance
Definition
 inherited ability of a weed or crop biotype to
survive a herbicide application to which the
original population was susceptible.
Biotype = a group of plants within a species that has
biological traits that are not common to the population
as a whole.
Herbicide Resistance
 cross resistance
* weed biotype that has gained resistance to
more than 1 herbicide with the same mode
of action. Same or different families.
 multiple resistance
* weed biotype that has developed tolerance
to more than one herbicide brought about by
different selection pressures (different
modes of action).
Why Are Plants Resistant to
Herbicides?
 altered site of action
 enhanced metabolism
 sequestration
Altered Site of Action
Source: J.L. Gunsolus. Herbicide Resistant Weeds. 1998.
North Central Region Extension Publication 468.
Herbicide Resistance

How does it occur?
Herbicide Resistant Weeds
Selection Pressure
Source: J.L. Gunsolus. Herbicide Resistant Weeds. 1998.
North Central Region Extension Publication 468.
Herbicide Resistance
Around the World
 304 Resistant Biotypes
182 Species (109 dicots and 73 monocots)
 over 270,000 fields
Source: Heap, I. The International Survey of Herbicide Resistant Weeds. Online. Internet.
October 20, 2005 .
The Beginning of Weed Resistance





Photo: The Missouri Flora Web-Site
1968 (Washington)
nursery crops
common groundsel
atrazine
simazine
Weed Characteristics That
Favor Resistance
 reproductive capability
 seed dispersal mechanisms
Worldwide
Source: Dr. Ian Heap (www.weedscience.com)
Average Number of Seed
Produced per Plant
450,000
400,000
400,000
350,000
300,000
250,000
200,000
150,000
100,000
50,000
40,000
40,000
9,000
goosegrass
annual
bluegrass
common
cocklebur
0
Palmer
Amaranth
Top 4 Herbicide Resistant Weeds in US
peanut - 175; cotton - 250; corn - 800
Herbicide Characteristics That
Influence Weed Resistance
 herbicides with a single site of action
 herbicides used multiple times during the
growing season
 herbicides used for consecutive growing
seasons
 herbicides used without other control
strategies
 repeated use of a product for more than 2
years could develop a herbicide resistance
problem!!
Herbicide Resistant Weeds
By Mode of Action
Commonly Used ALS Herbicides
 Accent
 Ally
 Beacon
 Cadre
 Classic
 Envoke
 Exceed
 Express








Harmony Extra
Peak
Permit
Pursuit
Python
Scepter
Staple
Strongarm
Herbicide Resistance in Georgia
Weed
Year
Herbicide
Location
goosegrass 1992
DNA
East GA
Prickly sida 1993
IMI
?
Italian
ryegrass
1995
Hoelon
Peach Co.
Hart Co.
Palmer
amaranth
2000
2005
SU/IMI
glyphosate
Burke Co.
Central GA
Other Counties in Georgia with ALSResistant Palmer Amaranth
 Tested by BASF in
2005
– Colquitt
– Cook
– Mitchell
 175 locations were
also sampled by UGA
weed scientists in
2005
* * *
Glyphosate Resistance Around the
World (8 species)








rigid ryegrass (1996)
goosegrass (1997)
horseweed (2000)
Italian ryegrass (2001)
hairy fleabane (2003)
buckhorn plantain (2003)
common ragweed (2004)
Palmer amaranth (2005)
Glyphosate Resistant Horseweed
in US (confirmed in 12 states)












DE (2000)
TN (2001)
IN (2002)
MD (2002)
NJ (2002)
OH (2002)
AK (2003)
MS (2003)
NC (2003)
OH (2003)
PA (2003)
CA (2005)
Horseweed pictures from SWSS Weed ID Guide
Other Weeds in the U.S. that have
Developed Resistance to Glyphosate
Palmer amaranth
(GA-2005)
Italian ryegrass
(OR-2004)
SWSS
SWSS
Common ragweed
(MO-2004)
USDA
L. Hall - UGA
Rigid ryegrass (CA-1998)
U.S. Acres Treated with Glyphosate
1996-2003
1996
1997
1998
1999
2000
2001
2002
2003
100
% of Acres
80
60
69
30
20
4 4 5 9 9 13 9 19
Corn
78
62 62
56 5758
40
0
73
46
36
2528
1314
Cotton
Soybean
Crop
Source: USDA - National Agricultural Statistics Service – Agricultural Chemical Usage Reports
Herbicide Resistance Should
Only Be Suspected When .……...
 other causes of herbicide failure have been
ruled out.
 the same herbicide or herbicides with the
same mode of action have been used year
after year.
 one weed that is normally controlled is not
controlled while other weeds are.
 healthy weeds are mixed with controlled
weeds (same species)
 a patch of uncontrolled weed is spreading.
MSMA Resistant Cocklebur in NC
(Dr. Alan York – NCSU))
Causes of Herbicide Failures
 weed size**
 rate
 moisture
 temperature
 humidity
 application method
 calibration
 others
All possible reasons for poor performance should be investigated
before considering the possibility of resistance!!!
Herbicide Resistant Weeds
Strategies for Control/Prevention
 proactive vs. reactive
 utilize other weed control tactics
(cultivation, row patterns, etc.)
 rotate herbicides with different MOA
 rotate crops
 scout fields
 prevent seed production
 clean tillage and harvesting equipment
How long does resistance last in
absence of further selection pressure?
100
98
75
%
 Andrews and Morrison
(1997) - Canada
 DNA resistant green
foxtail
 % of resistant seeds
after 7 years
 initial resistance was
at least 90%
87
81
50
25
0
0 DNA
1 DNA
DNA'a Applied in 7 years
Source: Weed Technology (1997): 11:369-372.
2+ DNA
Does the use of reduced rates influence the rate of
herbicide resistance development ?
 some say yes, some
say no
 single dominant gene
or multi-genic?
 Is level of control is
same?
 rate vs selection
pressure
 infrequent use of the
lowest rate that
provides effective
control
More Information About Herbicide
Resistance
 UGA Weed Science Web-Site
* http://gaweed.com
International Survey of Resistant Weeds
* http://www.weedscience.org/in.asp